Evidence for Plate Tectonics on Europa

byPaul GilsteronSeptember 11, 2014

It was the Galileo mission, which ended in 2003 when the probe descended into the depths of Jupiter’s atmosphere, that brought us the first solid evidence of an ocean beneath the ice of Europa. Galileo made multiple flybys of the Jovian moon, the first spacecraft to do so, with the closest pass being a scant 180 kilometers on October 15, 2001. As you would imagine, the radiation environment near Europa is hazardous, which is why the flybys were reserved for Galileo’s extended mission. We’ve been mining the Galileo data on Europa ever since.

You may remember that Galileo was unable to open its high-gain antenna on the way to Jupiter, so we had to rely on the ingenuity of mission controllers to get the maximum performance out of the low-gain antenna. That 70 percent of the mission’s science goals were still met, and that we are making new discoveries with the Galileo data today, still amazes me. Now we have new work on Europa that flags the evidence for plate tectonics on the distant moon, which would be the first sign of such activity on any world other than our own.

Simon Kattenhorn (University of Idaho) and Louise Prockter (Johns Hopkins University Applied Physics Laboratory) led this work, which offers visual evidence of the expansion of Europa’s icy crust. A look at Europa’s cracked and ridged surface as sent back by Galileo calls into question how the terrain formed, because while new crust is visible, the mechanism for destroying older crust is not apparent. Kattenhorn and Prockter suggest that this ‘missing terrain’ was absorbed into Europa’s ice shell rather than breaking through it into the ocean that lies beneath. But the evidence for plate tectonics is compelling, and the thickness of the ice shell remains controversial.

Image: Scientists have found evidence of plate tectonics on Jupiter’s moon Europa. This false-color image of the trailing northern hemisphere on Jupiter’s moon Europa — the hemisphere that faces away from Jupiter — shows numerous ridges (red) and band (light-colored) features. Subduction zones — regions where two tectonic plates converge and one is forced beneath the other — may also be present in the study area and are identified by arrows. Image credit: NASA/JPL/University of Arizona.

Plate tectonics describes the motion of large plates in the Earth’s outermost shell, causing earthquakes and volcanic activity as well as mountain-building and the formation of trenches in the oceans as the plates meet. Subduction can carry plate material back into the mantle, while new crust can emerge from seafloor spreading. On Europa’s surface, the break up of crustal material and its replacement by bands of fresh ice from below is apparent. The new material fills in broad bands that are kilometers wide. Kattenhorn and Prockter reconstructed what areas of the surface would have looked like before these disruptions occurred.

Just where was the old crust being destroyed so that the new crust could form? When the researchers looked at areas where subduction similar to Earth’s might be occurring on Europa, they found ice volcanoes on the overriding plate. The smoothness of the surface in these areas implied that older material was forced below rather than remaining as crumpled mountainous terrain on the surface. So now we have evidence not only of material moving up through the ice crust but a mechanism for moving surface material back into the shell.

Simon Kattenhorn comments on the significance of the finding:

“Europa may be more Earth-like than we imagined, if it has a global plate tectonic system. Not only does this discovery make it one of the most geologically interesting bodies in the solar system, it also implies two-way communication between the exterior and interior — a way to move material from the surface into the ocean — a process which has significant implications for Europa’s potential as a habitable world.”

Image: Scientists have found evidence of plate tectonics on Jupiter’s moon Europa. This conceptual illustration of the subduction process (where one plate is forced under another) shows how a cold, brittle, outer portion of Europa’s 20–30 kilometer (roughly 10–20 mile) thick ice shell moved into the warmer shell interior and was ultimately subsumed. A low-relief subsumption band was created at the surface in the overriding plate, alongside which cryolavas may have erupted. Image credit: Noah Kroese, I.NK.

Bear in mind the reason for Galileo’s fiery plunge into the Jovian atmosphere. The spacecraft, its systems degrading in the high-radiation environment, its fuel largely spent, was crashed into the giant planet so that there would be no possibility it might contaminate Europa at some point in the future with bacteria from Earth. Europa remains a target of high astrobiological interest, and preventing even the faintest possibility of contamination kept this fascinating moon pristine. We now ponder what kinds of equipment it might take to explore near-Europa space and the surface itself in hopes of finding evidence of life from below.

The paper is Kattenhorn and Prockter, “Evidence for subduction in the ice shell of Europa,” Nature Geoscience, published online 7 September 2014 (abstract). See also this JHU/APL news release.

Maybe we are over estimating the Europan environment to
as an abode for life to arise. Any proto-DNA type analogue would have to happen deep close to core, where more variety materials would be available for molecular assembly. If the Thickness of the Ice shell is 10km or in that range the vast majority of materials from any meteor or Comet strike will likely wind up at the core. My reasoning is that because Jupiter’s gravity they are likely to be high velocity strikes one can easily imagine a temporary ocean being created, leaving behind very little of the impact ‘Nutrients’ on the surface.
Even if by chance a primitive organism were to arise, how fast would that deep environment drive mutations created by reduced number of cosmic rays . We are taking about hundreds of miles of Water and 10 km (probably) of Ice above the ‘core’. I know there are champions of the idea of a nutrient stream finding it’s may from the surface ice to the ocean below.
While that may aid existing developed organism, it is not clear to me that the density involved Is capable of speeding up the actual rise of life.
I can more easily envision a Hitchhiking organism finding a home in the
deep Europan Ocean.

Global funding policy strikes me as increasingly odd. If you think about the redundancy of… deterrents… would it really make a difference if they would fill the warheads with junk? Its not meant to be used in any case. It would drive down maintenance costs considerably and free up funds for useful things that do actually make a difference, like, for an example, space exploration.

Doubtful regarding the survival of any microbes on Galileo because the probe burned up high in the Jovian atmosphere. Plus the orbiter spent years bathed in intense radiation surrounding Jupiter plus the regular harsh environment of space.

Yes we know of little creatures that can survive all this but it is doubtful they made the trip. Plus note that Galileo was sterilized as much as possible before leaving Earth, so while some microbes undoubtedly did make the journey whether they lasted long enough is another matter.

An even faster and less expensive option to get samples returned from Europa (which was discussed in a Centauri Dreams post a few months ago) is to use multiple flybys through the plumes of Europa first observed by HST. While subsequent observations have so far failed to reobserve the plumes, they might be a manifestations of plate tectonics described here.

Along similar line of thought to Rob Flores, is the rate of nutrient transfer significant to be of much use to life?

The subduction zone is acting the same way as a volcano on Earth, adding trace nutrients to the Europan ocean. But is this rate useful? The spectacular plumes we have observed are removing the nutrients. Is the balance reasonably symmetric, or is there a case that suggests net loss of nutrients?

Where the subduction might be useful, is if life arrived by panspermia, perhaps from early Mars or Earth. An impact in a subduction area might provide the needed mechanism to transfer life from near the surface to the subsurface ocean.

Alex: I don’t think we are necessarily dependent on the surface for nutrients. First of all, “nutrients” is a flexible concept. Each form of life has a different set, and by definition it is something that occurs in the environment. Second, I think the interior of the moon may have much greater potential as a source of nutrients than the surface. After all, planet (or moon) formation is a messy business and pretty much all the elements in protoplanetary cloud are going to be baked in to some extent. In other words, that subsurface ocean could be very salty and dirty, and I, at least, cannot think of any way how we would know (or think) that not to be the case.

About the plumes, unless there is reason to believe that they would be enriched in “nutrients” compared with the rest of the ocean, they would not result in a net decrease in nutrient concentration. If evaporation is involved in how the plumes are generated, you would in fact expect the opposite, the plumes to be more of a sink for water than anything else, causing a net increase in nutrient concentration. Probably a negligible effect in any case.

@ljk
“Plus note that Galileo was sterilized as much as possible before leaving Earth, so while some microbes undoubtedly did make the journey whether they lasted long enough is another matter.”

This is not true. Galileo was not sterilized AT ALL while on Earth, which is why the plan to crash it directly into Jupiter’s atmosphere was formulated, in an attempt to avoid forward contamination of the Jovian moons.

To quote:

“[…] and because it had not been sterilized to prevent biological contamination of the moons ‹no one had expected to find liquid water that far from the sun) this meant there was a small risk of contaminating Europa. So NASA and JPL agreed to destroy the spacecraft by directing it into Jupiter’s dense atmosphere, where it would be vaporized. Galileo’s flight team at JPL gave the old spacecraft its orders, and on September 21, 2003, it entered Jupiter’s atmosphere and was destroyed.”(http://www.jpl.nasa.gov/jplhistory/the80/jovian-t.php)

Thus, I am hopeful that some lifeform managed to survive, and during future exploration of Jove, we shall find the seeds of our exploration sprouted and blossoming into naturalized Jovians.

‘This is not true. Galileo was not sterilized AT ALL while on Earth, which is why the plan to crash it directly into Jupiter’s atmosphere was formulated, in an attempt to avoid forward contamination of the Jovian moons.”

I am stunned by this. Not only because they were dropping a probe into the planet’s atmosphere but because they DID know about the true state of the Galilean moons before the probe was launched in 1989. For crying out loud, they sterilized the Ranger lunar probes back in the day when they knew the chances of something living on Luna were slim.

Then Jo said:

“Thus, I am hopeful that some lifeform managed to survive, and during future exploration of Jove, we shall find the seeds of our exploration sprouted and blossoming into naturalized Jovians.”

I hope not, especially if there are any native lifeforms in the Jovian atmosphere. See here:

Even if there is no life on Jupiter anywhere, we should not be contaminating any world with terrestrial organisms at least until we can better examine each world first.

Finding extraterrestrial life is one of the most important goals in human knowledge. If we literally muddy the waters with terrestrial life the issue will remain confused at best. Look at what we have gone through with the Martian meteorite life debate:

It comes down to a matter of opinion. I don’t weigh a human being’s contamination of a world any differently than that of a meteorite or other circumstellar/protoplanetary dust and debris. Full-on-probe-Europa impact?–Yes, please. If we are the result of stellar evolution, then we are no more than agents of that system, interacting with our environment. Jupiter is no more or less a home to our biological family than Sol and Earth, the galaxy and universe. In my eyes, if Earth’s life can niche out an existence off-world, it has earned the right by proof of its resilience to survive. Not that our opinions matter, anyway. I just think it is a form of universal bigotry and blindness to think otherwise, to submit to a notion of consensus reality.

Most people are not genuinely worried about preexisting alien ecosystems; I suspect they are just afraid that a Xenomorph or Gremlin will pop up somewhere (a monster), or even better, a species more dominant, intelligent and sentient than we. Directed panspermia seems like the only way we would be able to influence ET in our favour; accidental panspermia may infer accidental results… Either way, it’s exciting!

Of course, increased public interest in cosmological exploration may occur if we found life elsewhere, assumptively uninfluenced by otherworldly intervention. But as enthusiastic hopefuls of the phenomenon already, we know better than to subject both terrestrial and extraterrestrial life to human morality and ethics. Just as a meteorite is free to bring about the mass extinction of entire species on Earth, so too should we expect this of other natural actualities; cultural exchanges between celestial bodies on multiple scales, if you will.

We can try to remotely control evolution, but must remember that evolution is still controlling us as the console in that process.

150km of descent in a hyperaccelerated environment seems like more than enough margin for error to take place. Maybe someone did know this and pretended denial to avoid stunned reactions. :)

Late to this thread, but I just wanted to second everything ljk said about not spreading Earth life to other worlds until we’ve studied them (and I would add, maybe never). I share his shock that we would send out unsterilized probes on any mission that has the remotest chance of contaminating an alien environment. There is so much we could destroy, so many questions we might never be able to answer.

(Submitted on 20 Jul 2014 (v1), last revised 26 Aug 2014 (this version, v2))
The hypothesis that Earth was intentionally seeded with life by a preceding extraterrestrial civilization is believed to be currently untestable. However, analysis of the situation where humans themselves embark on seeding other planetary systems motivated by survival and propagation of life reveals at least two ethical issues calling for specific solutions.

Assuming that generally intelligence evolves ethically as it evolves technologically, the same considerations might be applied to test the hypothesis of directed panspermia: if life on Earth was seeded intentionally, the two ethical requirements are expected to be satisfied, what appears to be the case.

“It comes down to a matter of opinion. I don’t weigh a human being’s contamination of a world any differently than that of a meteorite or other circumstellar/protoplanetary dust and debris. Full-on-probe-Europa impact?–Yes, please.”

Cripes, Jo – A meteorite with organic material might have hit Europa or some other world and snuffed out its native life so let’s just trash the place when we show up anyway? Seriously?

Yes coacervate, I get your hint. The real red stuff (not the false colour one) on Europa in neigh spectrally identical to archaea that are responsible for Earth’s red ice. Though no mineral match has ever been found that is as close, I doubt the search for life will turn out to be that simple (surely?)

Aside from all considerations, I believe it’s better not to think of things solely from an anthropomorphic point of view all the time. Matter is matter and unless someone [besides me] has a vision for a future where stellar evolution can be manipulated in a way that halts natural changes on universal scales (which I personally would be wholly against), let things go where they may, let people and things do as they wish. This is my view.

There’s another saying,

One man’s trash is another man’s treasure.

If I don’t weigh a human being any differently than a meteorite, then any guilt train will not suffice in changing my opinion of “trash” and what it might do to Europan life, or even other lives. My evolution has made it so that my opinion only changes when considering what is convenient, “whenever necessary conditions
occur”, to quote the Makukov & shCherbak paper I referenced also in an earlier CD post here: https://www.centauri-dreams.org/?p=31157#comment-120267

I believe it convenient being able to do what I want, without worrying about consequences outside of the non/deterministic wave of probability: chance. If a philosophy of morality is required by the universe (or supplemental to it), determined, then obviously none of our viewpoints matter–continue on as we were, the universe allows its own responsibility; the janitor of our compost. Win-win, when taking into account how patient one wants to be.

It is only healthy to play devil’s advocate. I’m not saying we should act as genocidal planetary bodies, I’m just saying we already are. Whether or not life is a rare event, we should continue on as if we are the gods and the universe our Petri dish–of course, that view being influenced through a low-patience focus; high-patience being ‘who cares’; the moderate view being more close to your vista and NS’.

It’s possible that Earth life is naturally spreading to other worlds. If so I would agree that this is a process we should study, not try to stop (even if we could, which is unlikely).

Unnatural spread of Earth life by human action is a different matter. This is foreseeable, to a great extent preventable, and may destroy things of irreplaceable value (both morally and scientifically) that would otherwise survive. Here on Earth similar events have been catastrophic. We should be doing everything we can to prevent it.

Correct me if I am wrong, but sometimes I get the feeling I am being snowed with philosophy and semantics to either avoid the real issue or give it a sense of weight without any real mass.

No we cannot stop the Universe from doing what it is going to do, but we CAN do our best not to contaminate other worlds with terrestrial life until we can at least do some initial exploring for native organisms. Nuff said.

I argue the extreme opposite position of you and NS. I am trying to get across the fact that if our species really cared about what you and NS are attempting to argue, then we would not be elated in sending ourselves or our probes to any planetary body at all; we would have developed technology that wouldn’t have required us to send things outside of our own atmosphere if we wanted to do “everything we can to prevent” potentially catastrophic events outside of Earth when we acquired the ability and awareness, if our sole mission is to learn–which it is not. Really, this is about expanding our territory to enhance our survival–which, if we are capable of learning from our past, then we already know what type of catastrophies to expect!

We don’t have the slightest clue about “doing everything we can to prevent” catastrophic events, because we are not in a position to dictate what is catastrophe as soon as we leave our own minds, our own societies. This comes from our own bias to survive, which I embrace, but am not foolish enough to think of in terms of right or wrong. The entire space program was developed to create in the minds of other members of our species a mutual sense of catastrophe. You don’t shoot first and then ask questions later–as your government has seemed fine doing, irregardless of any of your views. If knowledge of the Jovian system was as you say, then it appears as though the folks at JPL are closer to my view, totally fine with being allowed to do whatever they wish, with the people behind them, either out of ignorance, indifference, and/or support.

How can one pretend to care about an alien’s life when one didn’t even take the time to look at what NASA said about Galileo’s contaminated state before publicly making a comment about it? Where is the weight in that?

We are human beings: we make mistakes. I just don’t think it’s anything to be ashamed of. Just know that we are open to the judgment of other species if we are open to the judgment between ourselves, even ones who may be foreign to our planet, and we won’t evade that reality any less if we continue to expand while attempting to learn, without first knowing everything. Since that may be impossible, we make do and continue on Columbusing it–as we always have from the time observable life appeared. It isn’t really a choice, except between survival and extinction.

Additionally, what makes one think one is entitled to to explore or probe any organism besides oneself? Has anyone at NASA taken into account if the inhabitants of other worlds might want to be left alone and unexamined? There are human cultures that make a very big deal out of privacy and personal observation; it’s some kind of joke to try and act like you are standing for science or philosophy when both are tools created by a megalomaniacal species. Not that anything is wrong with that or matters, we should just maybe attempt to stay realistic–obviously people with those issues are still being observed, not only by their own species.

And I apologize if I make you feel some type of way; I enjoy discussions with you, with everyone.

Europa, Jupiter’s sixth-closest moon, has long been a source of fascination and wonder for astronomers. Not only is it unique amongst its Jovian peers for having a smooth, ice-covered surface, but it is believed that warm, ocean waters exist beneath that crust – which also makes it a strong candidate for extra-terrestrial life.

And now, combining a mosaic of color images with modern image processing techniques, NASA has produced a new version of what is perhaps the best view of Europa yet. And it is quite simply the closest approximation to what the human eye would see, and the next best thing to seeing it up close.

The high-resolution color image, which shows the largest portion of the moon’s surface, was made from images taken by NASA’s Galileo probe. Using the Solid-State Imaging (SSI) experiment, the craft captured these images during it’s first and fourteenth orbit through the Jupiter system, in 1995 and 1998 respectively.

The view was previously released as a mosaic with lower resolution and strongly enhanced color (as seen on the JPL’s website). To create this new version, the images were assembled into a realistic color view of the surface that approximates how Europa would appear to the human eye.

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last twelve years, this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

If you'd like to submit a comment for possible publication on Centauri Dreams, I will be glad to consider it. The primary criterion is that comments contribute meaningfully to the debate. Among other criteria for selection: Comments must be on topic, directly related to the post in question, must use appropriate language, and must not be abusive to others. Civility counts. In addition, a valid email address is required for a comment to be considered. Centauri Dreams is emphatically not a soapbox for political or religious views submitted by individuals or organizations. A long form of the policy can be viewed on the Administrative page. The short form is this: If your comment is not on topic and respectful to your fellow readers, I'm probably not going to run it.